Corporate users often desire to connect their portable computers (laptops or PDAs) to office networks at anytime from anywhere using wireless technologies. Until now, they have relied upon cellular networks to provide such “anytime, anywhere” connectivity. The data rate over current cellular networks is usually modest, e.g., 19.2 kbps in CDPD networks. Although 3 G cellular networks can support an aggregated data rate up to 2 Mbps for indoor/small cell or 384 kbps for wide area, it is unlikely that operators will allocate all the available bandwidth to serve data users, because voice is the major revenue source and thus most bandwidth will be reserved for voice calls. Therefore, it is expected that the practical data rate offered by 3 G cellular networks will be on the order of 100 kbps, which may not satisfy data users. Now, corporate users who want high-speed wireless connection can look for help from another wireless technology—the IEEE 802.11 WLAN (wireless local area network).
802.11 WLAN, a high-speed wireless data network standardized by the IEEE, was designed as a wireless extension of Ethernet. Since the 1999 release of the IEEE 802.11 standard, the 802.11b WLAN has been widely deployed in offices, homes, and public hot spots such as airports and hotels. Any portable computer with a WLAN card installed can be connected to these WLANs at a data rate up to 11 Mbps. In addition to high speed, WLAN has a number of other advantages, including ease of deployment (because it uses unlicensed spectrum) and low equipment cost. However, a serious disadvantage of WLAN is the small coverage area. An ordinary 802.11b AP (access point) can only communicate with 802.11b WLAN stations no more than 300 feet away.
WLAN and cellular data can be considered to be complementary wireless networking technologies to each other. WLAN has high speed but covers a small area, while cellular data networks provide wide-area coverage but at lower speed. It is very logic to integrate WLAN with cellular data networks for users, especially corporate users, who need high-speed wireless connection as well as anytime anywhere wireless connectivity. Thus, if a corporate user is under the coverage of a WLAN, his/her computer is connected to the WLAN and then to an office network; if there is no WLAN available, the computer is connected to a cellular network and then to the office network.
Currently there are two types of WLAN/cellular network integration solutions. One is operator-oriented and the other is enterprise-oriented. The objective of operator-oriented solutions is to bundle public WLAN service with cellular data service for cellular operators, where the authentication and billing method of the public WLAN service can reuse the cellular network infrastructure and resources, and thus users may receive some benefits due to integration, such as SIM card-based authentication and single bill service. Operator-oriented solutions provide wireless Internet service to both corporate users and consumers, but they are not one-stop, hassle-free wireless networking solutions for corporate users. After obtaining a wireless connection to the Internet through a cellular network or a public WLAN, a corporate user needs to run a VPN program to create a secure connection to the office network over the wireless connection and the Internet. Every time the user switches the wireless connection due to, for example, moving in or out of the range of the public WLAN, the secure connection is torn down and the user has to re-launch the VPN program. In addition, since operator-oriented integration solutions cannot include office WLAN and home WLAN, corporate users roaming between these WLAN environments and the integrated public WLAN have to frequently change WLAN configurations, including setting SSID (Service Set Identifier), enabling/disabling/setting WEP (Wired Equivalent Privacy) keys, and selecting proper device-level and user-level authentication methods. It has been known that getting these configurations right is a difficult task, especially for users who are not WLAN professionals. In order to solve the above problems for corporate users, enterprise-oriented WLAN/cellular network integration solutions have been proposed. The objective is to provide a secure connection between a corporate user's portable computer and the corporate network with mobility support across cellular networks and various WLAN, including office WLAN, home WLAN, and public WLAN, where the secure connection can remain alive after the wireless connection is switched due to the user's movement. The enterprise-oriented solutions are also called mobile VPN techniques by a number of vendors.